Photoperiod - what is the appropriate 'winter'?
 

Growing under lights, it is feasible to control intensity and duration (and, of course, temperature and humidity, as well as nutrient supplies). One can reduce winter (cooler, dryer, shorter days) to the minimum needed to initiate bud formation or dormancy requirements for those orchids with seasonal cycles. AOS publications suggest a 'several month' duration of shorter photoperiod for mixed collections or sensitive plants. My question is: what is the minimum time for this winter break? I'd rather see my plants growing fast, rather than idling in the cold and dark. Has anyone reduced winter to one month with success (for photoperiod sensitive orchids)?

There is no single correct answer. It depends a lot on what you are growing. What genera do you have now? Intend to acquire soon?

I am growing Cattleya, Phalaenopsis, Paphiopedalum, Phragmites, Dendrobium - and some others. As with most of us, it is a mixed collection.
I read that a period of reduced temperature may substitute for shorter photoperiod in initiating bud formation, but I have the same question about this - how short a cool period would do the job?

A general rule of thumb is to follow the seasons, so time the lights to seasonal lighting. My windowsill orchids don't get supplemental lighting and do well. I think that my under lights orchids roughly get about an hour more than those on the racks at the windows.

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But - since we can play 'Master of the World' in the totally artificial environment of a grow room, I'd like to supply conditions for maximizing growth without inhibiting flowering. Growing epiphytic orchids on a Chicago windowsill is artificial, you're just letting the sun (at that latitude) call the shots.

Look at the latitude where the specific orchid in question is found. The photo period each day of the year is easy to determine for a given latitude.

I think if you are looking for a general answer I would try about a two months period. I only gauge that by how long a Den nobile type orchid needs to rest before bud initiation


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Not so easy for multi-generic hybrids! Still, that's good guidance in general, but is rather conservative. Plants can respond to an early Spring by leafing out early, although they may get caught by a late frost. Similarly, orchids should be able to carry out dormancy and bud initiation in response to cooling temperatures and/or shorter photoperiods, in less than the full winter season. This might not serve them in a natural environment with variable weather, but that risk doesn't occur in a grow room. So, I still want to know how short the chilling and short day period needs to be.

Photoperiod - what is the appropriate 'winter'?
 

Before I grew my orchids out doors I set my grow room temp to min 60 and 12 hr grow light between Dec and Feb.
In that condition, all my nobile type dens initiated buds every year without issues.
Nobile type dens are highly seasonal growers and will only respond to a dry cool winter rest. I therefore used that as a guide line


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Two months sounds reasonable. I read that 4-5 weeks of cooling served to initiate flowering in Phalaenopsis, regardless of photoperiod. Any other bits of information out there?